The invention relates to a method for coating container bodies internally as they emerge in succession from a welding machine. The invention further relates to an apparatus for coating container bodies internally as they emerge in succession from a welding machine.
It is known to coat containers or container bodies internally with liquid or powder lacquers. Special problems arise in the coating of container bodies, particularly can bodies, emerging in succession from a welding machine in which the longitudinal seam of the bodies has been welded. If only the welded seam is to be covered, it is known to convey coating material through the welding machine and to apply it to the welded seam. However, if the whole of the internal wall of the container is to be coated, problems arise, as the deposition rate is only approximately 60%, which means that approx. 40% of the coating material, which is in the form of a mist of powder or liquid particles, does not remain, but escapes from the body, contaminating the conveyor line and its surroundings.
To give an indication of the level of this contamination, it can be stated as an example that in order to coat the weld seam only on the internal wall of the body of a 1/2 kg can 114 mm long, approximately 100 mg of powder coating material must be sprayed, of which, assuming the deposition rate to be as stated, 40 mg passes into the environment. With a daily production of 500,000 cans, this results in a considerable quantity of powder being discharged into the environment, and which, despite recycling by an external extraction system, may cause damage eg. to the bearings of the conveyor line, and even to those of the welding machine. If the container body is to be coated over its whole internal circumference, ie. over 360.degree., the quantity of powder involved will be increased several times more.